1. Field of the Invention
The present invention relates to a light emitting display, and more particularly, to a light emitting display in which a power supply line has a uniform voltage drop, thereby providing uniform display brightness.
2. Discussion of Related Art
Recently, various flat panel displays have been developed to replace cathode ray tube (CRT) displays, because CRT displays are relatively heavy and bulky. Flat panel displays include various types of light emitting display technologies including liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and light emitting diode displays (LEDs).
Among the light emitting display types, only LED displays can generate light, which is done through electron-hole recombination that allows a fluorescent layer of the LED to emit light. Light emitting displays are categorized into inorganic displays and organic displays according to constituent materials and structures. Flat panel displays and light emitting displays, generally, can be categorized into passive displays and active displays according to the driving mechanism. Active displays (e.g., LED displays) have the benefit of a fast response time like CRT displays in contrast to passive display devices (e.g., LCDs), which require a separate light source.
FIG. 1 is a view of a conventional light emitting display.
Referring to FIG. 1, a conventional light emitting display includes a substrate 10; a pixel area 20 including a plurality of pixels 21 placed on an area defined by scan lines S, data lines D, and pixel power source lines VDD formed on the substrate 10; a scan driver 30; a data driver 40; a first power source line 50; a second power source line 52; and a pad hub 60.
The scan driver 30 is placed adjacent to one side of the image display (e.g. pixel area 20), and electrically connected to a set of pads Ps on the pad hub 60 through a scan control signal line 32. The scan driver 30 generates a scan signal along the scan control signal line 32 and transmits the scan signal to the scan lines S of the pixel area 20 in sequence. For this, the scan driver 30 includes a plurality of shift registers to generate the sequential scan signals in response a scan control signal.
The data driver 40 is electrically connected to a second set of pads Pd on the pad hub 60 through a first data signal line 42, and connected to the data line D through a second data signal line 44. The data driver 40 can be mounted to the substrate 10 by a chip-on-glass method, a wire-bonding method, a flip chip method, a beam lead method, or similar technique, or directly formed on the substrate 10. The data driver 40 receives a data signal and a data control signal transmitted from the second set of pads Pd, and supplies the data signal corresponding to one horizontal line per one horizontal period to the data lines D on the basis of the data control signal.
The first power source line 50 is formed adjacent to a top side of the pixel area 20 and commonly connected to the one side of the pixel power source line VDD. The first power source line 50 receives a first power signal from the third set pads Pvdd on the pad hub 60 through the first signal line 58 and supplies a first power signal to the pixel power source line VDD of each pixel 21.
The second power source line 52 is electrically connected to a cathode electrode of a light emitting device formed on the whole surface of the pixel area 20. The second power source line 52 receives a second power signal from the fourth set of pads Pvss through the second signal line 56, and supplies the second power signal to the cathode electrode of the light emitting device.
One side of the pixel power source line VDD is commonly connected to the first power source line 50. The pixel power source line VDD supplies the first power signal from the first power source line 50 to each pixel 21.
Thus, each pixel 21 is controlled by the scan signal S transmitted by the scan line S. Each pixel 21 emits light using the current supplied to the light emitting device from the pixel power source line VDD in correspondence with the data signal of the data line D, thereby displaying an image.
However, in the conventional light emitting display, the pixel power source lines VDD that are commonly connected to the first power source line 50 are different in length from one another, so that the line resistance of the pixel power source lines is non-uniform, thereby supplying the power signal with differences in voltage drop (IR drop) to the respective pixels 21. For example, the closer a pixel 21 is to the first power source line 50, the less the voltage drop of the pixel power source line VDD. On the other hand, as a pixel 21 gets farther away from the first power source line 50, the voltage drop of the pixel power source line VDD is increased. Thus, in the conventional light emitting display, the voltage drop of the pixel power source line VDD is non-uniform according to the positions of the pixel 21, so that the amount of current available at any given pixel 21 selected by the same data signal varies according to the position of the pixel 21, thereby causing non-uniform brightness.